There are numerous known instruments of this type called lancets using a liquid jet. One of these instruments is for example described in the European publication No. 0 303 557 A3. The hand-operated instrument is equipped with a a manual control valve which is used to stop the pressurized flow of liquid during an operation. These valves are usually of complex construction due to the fact that they comprise at least one moving piece and a release spring designed to bring the moving piece back to its initial position. Due to this relative complexity, the handpiece becomes a costly piece which does not lend itself to being used once. However, the sterilisation requirements which are imposed on this type of instrument, and the problems posed when reusing it, particularly as regards the risks of contagion, make it virtually obligatory to use it once only.
Handpieces to be used only once already exist and are used in devices for irrigating and washing cuts, being supplied with a low-pressure or even air pressure liquid. Such handpieces are described for example in the American publications U.S. Pat. No. 4,519,385 and U.S. Pat. No. 5,147,292. Their design is completely incompatible with the technical constraints imposed in an instrument designed to dissect tissues and in which the pressure of the liquid can reach 70 bar.
Furthermore, the handpiece must have a ergonomic shape, fit in one hand and have all the function controls which can be operated easily using this hand's fingers. It must be possible to control it with one hand wearing a surgeon's glove, without the glove being subjected to constraints which might injure it. Furthermore, the fingers must be able to control the partial or total opening and closing of the jet of pressurised liquid instantaneously, quite effortlessly. The control manoeuvre has to be very flexible and quick given the precision requirements linked to the use of a lancet.
The main function of the handpiece is to control the supply and stop the supply of high-pressure liquid.
One advantageous secondary function is locking the liquid supply control in the stop position.
Finally, a third function is the suction function.